1. Field of the Invention
The present invention relates to a reel for coiling and uncoiling strips, particularly metal strips. The reel includes an expanding mandrel for the coil to be received. The expanding mandrel has at least shell-like spreading members, a spreader rod and spreading elements arranged between the spreading members and the spreader rod. A spreader cylinder is connected to the spreader rod and the expanding mandrel is driven by a drive motor with a control and computer unit for maintaining a predetermined winding pull or winding tension and for determining the outer diameter of the coil at any given moment.
2. Description of the Related Art
Reels of the above-described type are subjected to extremely high loads. In addition to the substantial weight of the coils of up to 45 tons in the case of steel coils, high winding pulls must be transmitted through the expanding mandrel to the respective coil. The spreading forces required for this purpose are generated by the spreader cylinder which is usually hydraulically operated. The spreader cylinder is rigidly connected to a mandrel shaft which surrounds the spreader rod. This spreader cylinder is operated by means of a pressure supply system with a feed pump.
The spreader cylinder and the spreading pressure are normally designed in such a way that a maximum coil with maximum coil weight can be coiled with maximum winding pull. In addition, the spreading pressure remains constant over the outer diameter of the coil at any given time. The winding pull is adjusted through the torque of the drive motor and is controlled in dependence on the outer diameter of the coil. The spreading forces which are inevitably also constant and relatively high when the spreading pressure is constant result in a significant wear of the spreading members and the spreading elements. Therefore, it is necessary to continuously check the reels and to disassemble the reels within relatively short intervals in order to replace the worn spreading components. Such a maintenance and repair of the reels is extremely time-consuming and expensive. In addition, due to the continuous maintenance of the maximum spreading pressure, for example, during uncoiling of a coil, the residual windings are damaged by afterspreading of the expanding mandrel and become useless.
When a strip is being coiled, an elastic winding pull is applied to the strip. As a result, radial forces act on the spreading members and the spreading elements. These radial forces continuously increase from winding to winding. The sum of these radial forces is particularly extremely high in those cases when thin and oiled or highly elastic metal strip, for example, aluminum strip is coiled. Although a self-supporting coiled ring is formed with increasing coil diameter, the high radial forces also lead to great wear or even failure of the spreading mechanism and subsequently to a collapse of the entire coil.
It is, therefore, the primary object of the present invention to provide a reel of the above-described type in which the service life of the expanding mandrel is substantially increased while avoiding premature wear and overloading.